Clinical and genetic epidemiological study of 16q22.1-linked autosomal dominant cerebellar ataxia in western Japan

Spinocerebellar ataxia type 31: A clinical and radiological literature review

Spinocerebellar ataxia type 31 (SCA31) is an autosomal dominant disease, classified amongst pure cerebellar ataxias (ADCA type 3). While SCA31 is the third most prevalent autosomal dominant ataxia in Japan, it is extremely rare in other countries. A literature review was conducted on PubMed, where we included all case reports and studies describing the clinical presentation of original SCA31 cases. The clinical and radiological features of 374 patients issued from 25 studies were collected. This review revealed that the average age of onset was 59.1 ± 3.3 years, with symptoms of slowly progressing ataxia and dysarthria. Other common clinical features were oculomotor dysfunction (38.8%), dysphagia (22.1%), hypoacousia (23.3%), vibratory hypoesthesia (24.3%), and dysreflexia (41.6%). Unfrequently, abnormal movements (7.4%), extrapyramidal symptoms (4.5%) and cognitive impairment (6.9%) may be observed. Upon radiological examination, clinicians can expect a high prevalence of cerebellar atrophy (78.7%), occasionally accompanied by brainstem (9.1%) and cortical (9.1%) atrophy. Although SCA31 is described as a slowly progressive pure cerebellar syndrome characterized by cerebellar signs such as ataxia, dysarthria and oculomotor dysfunction, this study evaluated a high prevalence of extracerebellar manifestations. Extracerebellar signs were observed in 52.5% of patients, primarily consisting of dysreflexia, vibratory hypoesthesia and hypoacousia. Nonetheless, we must consider the old age and longstanding disease course of patients as a confounding factor for extracerebellar sign development, as some may not be directly attributable to SCA31. Clinicians should consider SCA31 in patients with a hereditary, pure cerebellar syndrome and in patients with extracerebellar signs.

Spinocerebellar ataxias in Asia: Prevalence, phenotypes and management

This paper reviews and summarizes three main aspects of spinocerebellar ataxias (SCA) in the Asian population. First, epidemiological studies were comprehensively reviewed. Overall, the most common subtypes include SCA1, SCA2, SCA3, and SCA6, but there are large differences in the relative prevalence of these and other SCA subtypes between Asian countries. Some subtypes such as SCA12 and SCA31 are rather specific to certain Asian populations. Second, we summarized distinctive phenotypic manifestations of SCA patients of Asian origin, for example a frequent co-occurrence of parkinsonism in some SCA subtypes. Lastly, we have conducted an exploratory survey study to map SCA-specific expertise, resources, and management in various Asian countries. This showed large differences in accessibility, genetic testing facilities, and treatment options between lower and higher income Asian countries. Currently, many Asian SCA patients remain without a final genetic diagnosis. Lack of prevalence data on SCA, lack of patient registries, and insufficient access to genetic testing facilities hamper a wider understanding of these diseases in several (particularly lower income) Asian countries.

Insight Into Spinocerebellar Ataxia Type 31 (SCA31) From Drosophila Model

Spinocerebellar ataxia type 31 (SCA31) is a progressive neurodegenerative disease characterized by degeneration of Purkinje cells in the cerebellum. Its genetic cause is a 2.5- to 3.8-kb-long complex pentanucleotide repeat insertion containing (TGGAA)n, (TAGAA)n, (TAAAA)n, and (TAAAATAGAA)n located in an intron shared by two different genes: brain expressed associated with NEDD4-1 (BEAN1) and thymidine kinase 2 (TK2). Among these repeat sequences, (TGGAA)n repeat was the only sequence segregating with SCA31, which strongly suggests its pathogenicity. In SCA31 patient brains, the mutant BEAN1 transcript containing expanded UGGAA repeats (UGGAA_exp) was found to form abnormal RNA structures called RNA foci in cerebellar Purkinje cell nuclei. In addition, the deposition of pentapeptide repeat (PPR) proteins, poly(Trp-Asn-Gly-Met-Glu), translated from UGGAA_exp RNA, was detected in the cytoplasm of Purkinje cells. To uncover the pathogenesis of UGGAA_exp in SCA31, we generated Drosophila models of SCA31 expressing UGGAA_exp RNA. The toxicity of UGGAA_exp depended on its length and expression level, which was accompanied by the accumulation of RNA foci and translation of repeat-associated PPR proteins in Drosophila, consistent with the observation in SCA31 patient brains. We also revealed that TDP-43, FUS, and hnRNPA2B1, motor neuron disease–linked RNA-binding proteins bound to UGGAA_exp RNA, act as RNA chaperones to regulate the formation of RNA foci and repeat-associated translation. Further research on the role of RNA-binding proteins as RNA chaperones may also provide a novel therapeutic strategy for other microsatellite repeat expansion diseases besides SCA31.

Comorbid argyrophilic grain disease in an 87-year-old male with spinocerebellar ataxia type 31 with dementia: a case report

Background

Spinocerebellar ataxia type 31 (SCA31) is not usually associated with dementia, and autopsy in a patient with both conditions is very rare.

Case presentation

An 87-year-old male patient presented with ataxia and progressive dementia. Genetic testing led to a diagnosis of SCA31. Fifteen years after his initial symptoms of hearing loss and difficulty walking, he died of aspiration pneumonia. A pathological analysis showed cerebellar degeneration consistent with SCA31 and abundant argyrophilic grains in the hippocampal formation and amygdala that could explain his dementia.

Conclusions

This is the first autopsy report on comorbid argyrophilic grain disease with SCA31.

Inter-generational instability of inserted repeats during transmission in spinocerebellar ataxia type 31

The causative mutation for spinocerebellar ataxia type 31 (SCA31) is an intronic insertion containing pathogenic pentanucleotide repeats, (TGGAA)_n. We examined to what degree the inserted repeats were unstable during transmission. In 14 parent-child pairs, the average change of onset age was -6.4±7.3 years (mean±s.d.) in the child generation when compared with the parent generation. Of the 11 pairs analyzed, six showed expansion of inserted repeat length during transmission, and five showed contraction. On average, the inserted repeats expanded by 12.2±32.7 bp during transmission, but their mean length (with a 95% confidence interval) was not significantly different between parent and child generations. We consider that the length of the inserted repeats in SCA31 is changeable during transmission, but inter-generational instability is not marked, as far as the current sizing method can determine.

Autopsy case of spinocerebellar ataxia type 31 with severe dementia at the terminal stage

Spinocerebellar ataxia type 31 (SCA31) is an autosomal dominant cerebellar ataxia commonly observed in Japan. However, few neuropathological examinations have been conducted. Here we report the case of a 76-year-old Japanese male SCA31 patient. He noticed dysarthria and difficulty walking at 65 years old. His symptoms subsequently deteriorated, although he could still walk with assistance at 70 years. At 73 years, when he could no longer walk, he was admitted to our hospital. He showed severe limb and truncal ataxia. His father and older brother had shown the same symptoms. Brain magnetic resonance imaging showed cerebellar atrophy of the anterior lobe and white matter hyperintensities. He was diagnosed with SCA31 by genetic analysis. Gradually, his cognitive functions and ability to communicate declined. He died of respiratory failure at the age of 76. Neuropathological examination revealed severe Purkinje cell loss that was accentuated in the anterior lobe of the cerebellum. Furthermore, the remaining Purkinje cells showed abnormal processes (that is, halo-like amorphous materials), as has been reported previously. Severe deposition of hyperphosphorylated tau-positive neurites, many senile plaques and amyloid angiopathy were observed in the neocortex. Our findings suggest that in SCA31, accelerated tau and amyloid pathology in the neocortex might induce dementia at the terminal stage.

[A case of 77-year-old male with spinocerebellar ataxia type 31 with left dominant dystonia]

We report on the case of a 77-year-old male with genetically proven spinocerebellar ataxia type 31 (SCA31) who had dystonia. He was referred to our hospital for evaluation following a 6-year history of slowly progressive unsteadiness of his left leg during walking and dysarthria at the age of 62 years old. On the basis of his symptoms, we diagnosed him as spinocerebellar degeneration (SCD), and prescribed taltirelin hydrate. However, his symptoms continued to worsen. He required a cane for walking at the age of 63 years, and a wheelchair at the age of 66 years. He was admitted to our hospital following acute cerebral infarction at the age of 77 years. On examination at admission, right hemiparesis and cerebellar ataxia were detected. And left hallux moved involuntarily toward the top surface of the foot at rest, that is dystonia. The dystonia was not associated with cerebral infarction, because it had been several years with dystonia that he got cerebral infarction. Genetic analysis revealed that this patient harbored a heterozygous SCA31 mutation. Previously there have been no reports of SCA31 associated with dystonia. Our case report support clinical heterogeneity of SCA31, and highlight the importance of considering this type in patients with dystonia and ataxia. Patients with the combination of dystonia and ataxia and a family history of a neurodegenerative disorder should be tested for SCA31.

[Clinicoepidemiological analysis of genetic testing in 1,000 cases of hereditary neurological disorders]

A total of 1,000 neurological patients were examined for genetic testings at the Department of Neurology, Okayama University, from 1992 to 2010. To investigate the role and significance of genetic testings in neurological diagnostic consultation, we divided the analysis period into two, the former period (1992 to 2000) and the latter period (2001 to 2010). The number of genetic testings was 669 cases in the former period, and 331 cases in the latter period. However, the positive rate of genetic testings was 25.3% in the former period, and 48.1% in the latter period. The reason of this remarkable rise of the positive rate in the latter period was mainly attributable to our feedback inquiry to the doctors from 2001, noticing them the total number of test in a year, positive rate with or without family history, and an encouragement to examine more clinical details of their patients. The genetic testing plays an essential role in clinical neurology. It is important that the application of genetic testing to each case should be considered more carefully and properly.

Analysis of an insertion mutation in a cohort of 94 patients with spinocerebellar ataxia type 31 from Nagano, Japan

Spinocerebellar ataxia type 31 (SCA31) is a recently defined subtype of autosomal dominant cerebellar ataxia (ADCA) characterized by adult-onset, pure cerebellar ataxia. The C/T substitution in the 5′-untranslated region of the puratrophin-1 gene (PLEKHG4) or a disease-specific haplotype within the 900-kb SCA31 critical region just upstream of PLEKHG4 has been used for the diagnosis of SCA31. Very recently, a disease-specific insertion containing penta-nucleotide (TGGAA)_n repeats has been found in this critical region in SCA31 patients. SCA31 was highly prevalent in Nagano, Japan, where SCA31 accounts for approximately 42% of ADCA families. We screened the insertion in 94 SCA31 patients from 71 families in Nagano. All patients had a 2.6- to 3.7-kb insertion. The size of the insertion was inversely correlated with the age at onset but not associated with the progression rate after onset. (TAGAA)_n repeats at the 5′-end of the insertion were variable in number, ranging from 0 (without TAGAA sequence) to 4. The number of (TAGAA)_n repeats was inversely correlated to the total size of the insertion. The number of (TAGAA)_n repeats was comparatively uniform within patients from the three endemic foci in Nagano. Only one patient, heterozygous for the C/T substitution in PLEKHG4, had the insertions in both alleles; they were approximately 3.0 and 4.3 kb in size. Sequencing and Southern hybridization using biotin-labeled (TGGAA)₅ probe strongly indicated that the 3.0-kb insertion, but not the 4.3-kb insertion, contained (TGGAA)_n stretch. We also found that 3 of 405 control individuals (0.7%) had the insertions from 1.0 to 3.5 kb in length. They were negative for the C/T substitution in PLEKHG4, and neither of the insertions contained (TGGAA)_n stretch at their 5′-end by sequencing. The insertions in normal controls were clearly detected by Southern hybridization using (TAAAA)₅ probe, while they were not labeled with (TGGAA)₅ or (TAGAA)₅ probe. These data indicate that control alleles very rarely have a nonpathogenic large insertion in the SCA31 critical region and that not only the presence of the insertion but also its size is not sufficient evidence for a disease-causing allele. We approve of the view that (TGGAA)_n repeats in the insertion are indeed related to the pathogenesis of SCA31, but it remains undetermined whether a large insertion lacking (TGGAA)_n is nonpathogenic.

High frequency of Machado-Joseph disease identified in southeastern Chinese kindreds with spinocerebellar ataxia

Background

Machado-Joseph disease (MJD), caused by a CAG repeat expansion located in exon10 of the ATXN3 gene, is now regarded as one of the most common spinocerebellar ataxia (SCA) in the world. The relative frequency of MJD among SCA has previously been estimated at about 50% in the Chinese population and has been reported to be related to the frequency of large normal alleles in some populations. Taq polymerase has been used for PCR in nearly all studies reported previously.

Methods

Normal and expanded alleles of ATXN3 were detected via PCR using LA Taq DNA polymerase (better for GC-rich sequences) and denaturing polyacrylamide gel electrophoresis in 150 normal individuals and 138 unrelated probands from autosomal dominant SCA families. To compare reaction efficiency, 12 MJD patients' expanded alleles were amplified with La Taq and Taq polymerase respectively in the same amplifying systems and reaction conditions.

Results

Normal alleles ranged from 12 to 42 CAG repeats. The most common allele contained 14 repeats with a frequency of 23.3%, which corroborates previous reports. The frequency of large normal alleles (>27 repeats) was 0.28, which was very high relative to previous reports. The frequency of MJD in SCA patients was 72.5%, which was significantly higher than those in previous reports about the Chinese and other Asian populations. This frequency was one of the highest reported worldwide, with only Portuguese and Brazilian populations exhibiting higher proportions. All 12 expanded alleles were amplified in PCR with La Taq polymerase, whereas only 2 expanded alleles were amplified with Taq polymerase.

Conclusion

We have first reported the highest relative frequency of MJD in Asia, and we attribute this high frequency to a more efficient PCR using LA Taq polymerase and hypothesized that large ANs may act as a reservoir for expanded alleles in the Southeastern Chinese population.